The present invention is directed to an apparatus for the production of squared timber from round logs by severing or slicing, without forming any cuttings such as chips or sawdust, a series of strips or boards from opposite sides of the log by utilizing two opposed banks of staggered cutting blades. The apparatus will include a feeding device or means for moving the log axially in a longitudinal direction through the oppositely placed banks of cutting blades with the blades in each bank being arranged in staggered relationship with greater penetration into the log or workpiece as the distance along the feed direction increases. The banks of blades are oscillated during the cutting operation and each bank of blades includes a pressure pad immediately preceding a cutting edge of each blade and a guide strip contacting the processed surface of the log being provided immediately ahead of the pressure pad. Preferably, in addition to the pressure pad and guide strip for each blade, a guide strip is also immediately following the last blade in each bank.
An apparatus for producing straight timber from round logs and also from flattened logs and squared timbers so that an central region of the log is processed into a squared timber and the log segments which lie outside of the squared timber are separated into boards at two mutually opposite sides of the log in a non-chip-forming fashion by utilizing a plurality of intermediately succeeding cutting operations spaced along the direction of feed of the log is disclosed in U.S. Pat. No. 4,086,944 which claims priority from German patent application P 25 14 901 and also in U.S. Pat. No. 4,220,185 which claims priority from German patent application P 27 51 238. Reference is made to these two U. S. patents for a more detailed explanation of the structure and positioning of the cutting blades, the structure of the guiding arrangement and feed means, the structure for obtaining the oscillation of the cutting blades and the positioning of both pressure pads and guide strips or pads. Thus, the present application incorporates the disclosure of these two patents by reference thereto.
The lateral separation of boards or strips from a log without forming any chips or sawdust is very desirable for the reasons of waste which is eliminated by the process and the process involves a variety of technical difficulties. If it was not for these difficulties, such a method would otherwise certainly have prevailed earlier in the prior art. One of the greatest problems is obtaining an acceptable, faultless product surface since the risk of premature splitting and tearing of the wood exists given non-chip-forming severing or slicing of the boards by means of a cutting operation with blades having a finite thickness.
In order to avoid this, additional guide strips for each of the banks of blades was proposed in the U.S. Pat. No. 4,220,185. These additional guide strips are disposed between the blades of the bank and the pressure pad which is seated immediately in front of the cutting edge of the next following blade.
Whereas the pressure pads are provided for the purpose of exerting pressure on the surface of the wood in the immediate proximity of the cutting edge of the blade in order to prevent a premature splitting of the next board or strip that is being produced and accordingly only provides a relatively small pressure face, the additionally interposed guide strips have a significantly larger seating surface in comparison to the pressure pads since they are not so much intended to exert a high topical pressure as to guide the workpiece back into the desired alignment before the next severing operation in case the workpiece or log should exhibit a tendency toward lateral excursion, for example, due to differing wood hardnesses at the two sides of the log. It has been shown that an acceptable surface quality of the separated boards can usually not be achieved without using this additional guidance. Further, the guide strips exercise a smoothing effect on the exterior wood surface when it is additionally considered that these guide strips, due to their rigid attachment to the oscillating frame of the bank of blades not only executes a relative motion in the feed direction but over and in addition to this also execute a circular oscillatory motion which at least proceeds at an angle relative to the feed means.
Given the apparatus known from the two above cited patents, the two lateral blade groups or banks are rigidly set to a defined lateral spacing relative to the longitudinal axis of the feed path in accordance with the log diameter which is being processed and also in accordance with the thickness of the squared timber which is to be finally produced. While the U.S. Pat. No. 4,220,185 states that the guide surfaces exert pressure on the log from both sides, it should be noted that this pressure is essentially generated by reaction of the elastic wood material itself. This becomes clear when one examines the arrangement of the blades and the guide strips in the drawings of the patent and also the attached drawings. Given the known manner of proceeding, the guide strips, which are positioned ahead of the first blade, were originally set such that their lateral spacing corresponds to the dimension of the log, which is usually flattened in advance, and the guidance under a defined pressure would be achieved by means of a slight constriction relative to the log diameter. The pressure effect of the other guide strips was defined on the other hand by the graduation of their settings within the blade frame of each bank of blades as well as by the adjustment of the blades. When a specific blade removes more wood than intended, then the contact pressure of the following guide strips will be reduced as a result. On the other hand, the wood has a certain resilient effect so that there is still a pressure effect between the wood and two oppositely disposed guide strips given proper adjustment of the blade and following guide strips.
As may be derived from the above comments, the conditions upon employment of the additional guide strips can continue to be relatively undefined and this condition may have a deleterious effect on the quality of the product being produced. It must also be considered that the difference of the changing pressure of the pressure pads and guide strips also influence their frictional losses on the wood surface and thus influence the power consumption of the oscillating drive of the banks of blades or cutters and has an overall effect on the power consumption of the feed drive.